The present invention relates to a pulse generator of the current injection type using the Josephson junctions, and more particularly to improvements thereof for generating pulses of very short width without causing resonance and for enabling high density integration.
To realize a high-speed computer with low power consumption using the Josephson junction integrated circuit, not only must the memory circuit, logic circuit and control circuit making up the computer operate with a short access time or cycle time but also the pulse rise time and pulse fall time as well as the pulse width must be short.
In order to satisfy this requirement a pulse generator using the Josephson junctiors has been proposed in a publication "A Josephson ultrahigh-resolution sampling system", David B. Tuckerman, Appl. Phys. Lett. 36(12), 15 June 1980, pp 1008 to 1010. This circuit is composed of a combination of an interferometer logic gate circuit and a single Josephson junction. In this pulse generator, in response to an input current the gate circuit being supplied with a gate current is switched into the voltage state to inject the gate current into the single Josephson junction, thereby producing the injected current as an output current. When the injected current exceeds the critical current of the Josephson junction, the Josephson junction is switched into the voltage state so that the output current is cut off. As a result, there is obtained the output pulse current whose rise time is given by the switching time of the interferometer logic gate circuit and fall time is given by the switching time of the single Josephson junction.
However, a large chip area is required to form the inductance component necessary to magnetically couple the input current in the interferometer logic gate circuit, and the accurate control of the inductance value is difficult. A closed loop including the above inductance and the capacity of the Josephson junction in the gate circuit causes a resonance which should be damped. Further, such a gate tends to trap stray magnetic flux when switched to the superconducting state, resulting in malfunctions.